It is known to sinter and machine such metals as tungsten and its alloys to be used as high-density balancing weights or the like. These are relatively expensive to produce and for many purposes, such as fishing line weights, the more traditional cast lead is used, this material being capable of being deformed by pinching to grip the fishing line. It has also been proposed to manufacture fishing weights by adding lead powder to a settable or mouldable material, to produce a formed weight adapted to have the fishing line tied around it (U.S. Pat. No. 3,192,662) or to produce a pliable mass that is shaped on the line (U.S. Pat. No. 3,638,347 and GB No. 2 048 631A) or on a tubular core member (U.S. Pat. No. 3,782,025).
The use of lead has a number of disadvantages. Particular concern has been expressed in recent years about the toxic effects of lead on wildlife, particularly near freshwater fishing sites. Also, lead weights particularly in the smaller sizes are awkward to handle and are inconvenient to fix onto or release from a fishing line, because it is necessary to deform the material to clamp it onto the line. As regards the weights proposed in U.S. Pat. No. 3,192,662, these require a degree of dexterity to attach them to a line and each will be suitable for only a narrower range of line thicknesses. The pliable weights that have been proposed are liable to be easily loosened or detached if they encounter an obstacle in the water or due to the forces acting on them when the line is cast.
The release of lead into the wild-life cycle can also occur through the shot of shotgun cartridges, or the pellets of air guns. In this area also there is a need, therefore, for a non-toxic high-density material that can be economically formed to the required shape. Attempts have been made to use steel as a substitute material, but with limited success.
As regards fishing weights, it has also been proposed to make these with a core consisting of a wolframite mass in an outer jacket (U.S. Pat. No. 3,852,907). Such weights are mainly usable only as sinkers, since they do not grip the fishing line, but a construction is described in the patent specification that allows the weight to be fixedly clamped on the line because the outer jacket is of lead and has a cusp-like indent by which it is crimped onto the line. It may be noted in this last example, therefore, that although a major part of the mass is of wolframite, the outer lead jacket presents substantially the same toxic hazard as a weight made wholly of lead. Moreover, this form of weight will either require considerable force to clamp it firmly onto the line or will be susceptible to gross deformation limiting its capability for reuse.